Palestinian militants bombarded southern Israel with dozens of rockets and mortar shells Tuesday, while Israeli warplanes struck targets throughout the Gaza Strip in the largest flare-up of violence between the sides since a 2014 war.

The Israeli military said most of the projectiles were intercepted, but three soldiers were wounded, raising the chances of further Israeli retaliation. One mortar shell landed near a kindergarten shortly before it opened.

The sudden burst of violence follows weeks of mass Palestinian protests along the Gaza border with Israel. Over 110 Palestinians, many of them unarmed protesters, have been killed by Israeli fire in that time. Israel says it holds Gaza’s Hamas rulers responsible for the bloodshed.

“Israel will exact a heavy price from those who seek to harm it, and we see Hamas as responsible for preventing such attacks,” Israeli Prime Minister Benjamin Netanyahu said.

Israel and Hamas are bitter enemies and have fought three wars since the Islamic group seized control of Gaza in 2007.

The last war in 2014 was especially devastating, with over 2,000 Palestinians killed, including hundreds of civilians, and widespread damage inflicted on Gaza’s infrastructure in 50 days of fighting. Seventy-two people were killed on the Israeli side.

Tuesday’s violence bore a striking resemblance to the run-up to past wars. In the early morning, Palestinian militants fired over two dozen mortar rounds into southern Israel, including the shell that landed near the kindergarten.

The Israeli military said it carried out over 35 airstrikes on seven sites across Gaza, including an unfinished tunnel near the southern city of Rafah that crossed under the border into Egypt and from there into Israeli territory. No Palestinian casualties were reported.

Palestinian militants continued to fire additional barrages toward southern Israel, setting off air raid sirens in the area throughout the day and into the evening.

Brig. Gen. Ronen Manelis, the chief military spokesman, threatened tougher action and said it was up to Hamas to stop the situation from escalating.

“These strikes will continue to intensify as long as necessary if this fire continues,” he told reporters outside Israeli military headquarters.

They said Israel “began this round of escalation” by targeting their installations in the past two days, killing four militants. It was the first time the armed wing of Hamas has claimed responsibility for rocket attacks out of Gaza since the 2014 war.